Something I have pondered my entire career. You would think since every retail box shopping center in the US now gets built with a rather large canopy along the front of the building, that this would be something that would come up more often in conversation. What about porte-cochere structures in front of hotels and home improvement stores that are attached to the main building? Are these overhangs or open structures or a bit of both??
In the absence of better guidance from ASCE 7 on this subject, I have always defaulted to the most conservative wind loading- overhang pressures. I think the portion of the roof overhang adjacent to the building will have the highest underside (upward) pressure on the ceiling/soffit because the wind is hitting the wall of the structure and then going upwards and there are localized high pressure zones. However, as you get further away from the building wall this pressure likely diminishes. But how much? I think at some point it transitions into behaving more like an open structure with very little upward pressure on the ceiling/soffit. I have heard some suggestions like out 10-15 feet you could switch over to open roof loading pressures. I would not argue with this logic either, and may have taken similar approaches in the past. Or maybe I am way off here...
